You do not have to pay to use Ancestry.com for family mapping. You only pay if you use the research service.
If your brother has everything in place, he can add you as a user and you can add or edit what is there. Alternatively, you can build yours and he can then merge the two. One other option is he exports and sends his tree to you as a file, you rename it and add your material. Then you upload everything and keep it wholly separate from his.
My two cousins and I have taken this last approach. One cousin from my mothers side had her ancestry traced but also his mother's which I did not care about. The other cousin had my Fathers but also his wires family - once again I wasn't interested. He is also very particular about what he will recognize as proof. His standards sometimes become near impossible once he got to the mid/early 1800's. I compiled both sides into one and added material that I believed to be accurate. The biggest issue with this last approach is getting photos to transfer - I have had to reattach numerous pictures and maps to individual names.
Good luck
You can tell a lot about a woman by her hands...
- For example, if they are wrapped around your throat she's probably slightly upset.